1. Field of the Invention
The present invention relates to a process for the preparation of gabapentin and, more particularly, it relates to a process for the purification of gabapentin hydrochloride and for its conversion into gabapentin by treatment with a strong cationic ion exchange resin.
2. Description of the Background
Gabapentin, 1-(aminomethyl)cyclohexaneacetic acid (The Merck Index, XII Ed., page 733, No. 4343), is a known drug with anti-epilectic activity described for the first time by Warner-Lambert Co. in the U.S. Pat. No. 4,024,175.
In the literature several processes for the preparation of gabapentin are reported (see for example the U.S. Pat. Nos. 4,024,175, 5,068,413 and 5,091,567).
Substantially all these methods foresee a final step of gabapentin purification that consists in the treatment of an aqueous solution of a gabapentin salt (generally hydrochloride) through a weak basic ionic exchange resin, the complete evaporation of water from the aqueous gabapentin solution eluted from the resin and the crystallization from an alcoholic solvent, generally methanol or methanol/isopropanol or ethanol/ether mixtures.
Several alternative methods to the use of the weak basic ionic exchange resin for the conversion of gabapentin hydrochloride into gabapentin have been described.
In patent application WO 98/28255 (Teva) a process for the preparation of gabapentin from the corresponding hydrochloride is described which comprises the purification of gabapentin hydrochloride from the inorganic salts deriving from the synthesis by (a) solubilization of gabapentin hydrochloride in organic solvents wherein the inorganic salts are insoluble, (b) filtration and (c) optional evaporation of the solvent; the treatment of a gabapentin hydrochloride solution with an amine in a solvent so as to precipitate gabapentin form III and the crystallization to obtain gabapentin form II.
In patent application WO 00/58268 (Bioindustria Laboratorio Italiano Medicinali S.p.A.) the separation of the inorganic salts from gabapentin is carried out by diafiltration.